It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1658 = 2 ⋅829.
It is a cyclic number.
It is an alternating number because its digits alternate between even and odd.
It is a Duffinian number.
It is a Curzon number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 8561.
28561 is an apocalyptic number.
It is an amenable number.
8561 is a wasteful number, since it uses less digits than its factorization.
8561 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 1230.
The square root of 8561 is about 92.5256721132. The cubic root of 8561 is about 20.4569789847.
Subtracting from 8561 its reverse (1658), we obtain a triangular number (6903 = T117).
The spelling of 8561 in words is "eight thousand, five hundred sixty-one".